The present invention relates to a method of alloying an interface between a semiconductor and a metal layer, thereby forming an ohmic contact, and to a wiring forming method, a display unit forming method, and an image display unit fabricating method using the alloying method.
In the case of forming a metal layer as an electrode on a semiconductor device, it is required to convert a portion, being in contact with the semiconductor device, of the electrode into an ohmic contact to the semiconductor device. The conversion of a portion of an electrode into an ohmic contact has been typically performed by thermally alloying the portion of the electrode with the semiconductor device. For example, in the case of converting a portion, being in contact with an n-GaAs layer of a semiconductor device, of a contact metal AuGe/Ni/Au into an ohmic contact, the semiconductor device is heated at 420° C. for about one minute, to alloy the portion of the contact metal with the n-GaAs layer of the semiconductor device.
In the case of forming an ohmic contact by the so-called thermal alloying technique as described above, since the entire semiconductor device is heated, characteristics of the semiconductor device may be degraded. For example, to alloy an interface between the n-GaAs layer and the contact metal AuGe/Ni/Au for converting the interface into an ohmic contact, as described above, it is required to the entire semiconductor device at 420° C. for about one minute. In this case, if the n-GaAs layer is directly formed on a GaAs substrate, there is no problem; however, if an epitaxial layer not withstanding the above heating temperature is formed under the n-GaAs layer, or if an insulating film made from a resin or the like is formed before formation of a contact metal, there may occur a problem that device characteristics may be degraded by the thermal alloying process.
In view of the foregoing, an alloying process using laser irradiation has been proposed, for example, in Japanese Patent Laid-open No. Sho 57-72322. The alloying process using laser irradiation, which allows local heating, is expected to extend the application range and reduce degradation of the performance of a semiconductor device. The alloying process using laser irradiation, however, has problems that the irradiation of a laser beam having a high energy may cause abrasion of the surface of a metal and a semiconductor and damage the inner structure of a device, and that the irradiation of a laser beam having a high energy required for alloying limits an irradiation area, to reduce the throughput, thereby increasing the production cost.